1. Field of the Invention
The invention relates to a vacuum excavation system of the type which uses high velocity air to loosen the soil and a pneumatic vacuum to remove the loosened soil, and in particular, to an air vacuum excavation system having an improved air powered vacuum apparatus including an injector assembly for reducing the sound level of the supersonic air traveling through the air powered vacuum apparatus and creating a powerful vacuum in the spoil or material collection container for drawing the spoil or material into the container.
2. Description of Related Art
Vacuum excavation systems are well known. U.S. Pat. Nos. 4,776,781; 4,936,031; 5,140,759; 5,361,855; and 6,000,151 disclose pneumatic soil excavation systems in which a jet of air is directed against a mass of soil by a hand-held nozzle to cause the mass to break up, and in which the loosened soil is collected by entraining it in an air flow carried by a pipe or conduit, and depositing the entrained soil at a site away from the excavation.
Air vacuum excavation systems can safely uncover any type of buried object. These prior art systems that are provided by the assignee of this patent application use a synergistic combination of supersonic jets of air and high flow pneumatic vacuum transport. Supersonic air jets are extremely effective for penetrating most types of soil, and are harmless to all types of non-porous buried objects. That is, these supersonic air jets can be used to uncover, without fear of damage or disruption to gas, water or sewer pipes; electric or fiber optic cables; hazardous waste tanks, drums, boxes, cartons or bottles; or unexploded ordnance such as bombs or mines. Soil traditionally is not material that can easily be vacuumed, and therefore, it needs to be handled efficiently and effectively.
Safe soil excavation becomes more important daily, especially to industry and government. Commercial contractors, using conventional excavation equipment for locating buried utility equipment, such as wires, cables, etc., can have hundreds of accidents each year involving major property damage and loss of life. Accidental severing of a transcontinental fiber optic line may cost the industry over $1.5 million per hour in lost revenue. Additionally, federal and local governments may have a priority for environmental remediation to return land to the public in a clean and useable condition. Landfills can have over 4 million cubic yards of buried waste contaminated with hazardous and radioactive substances. Military operations conducted at test or impact ranges and training or detonation areas can have millions of acres of government owned property buried with unexploded ordnance. It has been demonstrated that the use of conventional excavation equipment may be too dangerous, resulting for example, in deterioration of buried drums or detonation of buried unexploded bombs and shells.
Above-discussed U.S. Pat. No. 6,000,151 discloses a vacuum excavation apparatus having an air lance for directing air at supersonic speeds at a material to be excavated and a material pickup hose for removing the loosened dirt from the excavation. The pickup hose is connected to a vacuum engine which is attached to an airtight material collection drum and which is operated by a foot operated air valve. The air supply for the vacuum engine and the air supply for the air lance are supplied by compressed air hoses from a single portable air compressor, which may be located in near proximity or may be remotely located, i.e., over 200 feet away from the vacuum engine and the air lance.
Air powered venturi vacuums are well known. Several varieties of drum top vacuums may be purchased commercially. These generally consist of a lid attached to a material collection drum, a suction generating device mounted on the lid, a compressed inlet air connected to the suction device, an air suction inlet means and an air discharge means. A 55 gallon drum full of soil can weigh over 700 pounds and can be very difficult to empty. There may or may not be an inlet or outlet filter and/or a discharge silencer associated with the vacuum engine and/or material collection drum.
U.S. Pat. No. 6,000,151 also discloses a vacuum engine as having a multistage venturi ejector with an exit discharge bag. The device of the '151 patent is sold commercially under the UTILIVAC® trademark. This ejector uses a complicated system of internal valves to direct the suction air through a particular chamber section in order to change the head/flow relationship. Another example of a multistage venture ejector system is commercially available under the Norclean trade name. This system also employs a complicated arrangement with multiple jet pumps in parallel where compressed air passes through specially designed nozzles and venturi pipes at supersonic velocity.
It is known that the excavation and vacuum transport of soil has its own unique set of characteristics. For example, soil types vary widely in grain size, particle shape, packing, moisture content, grading, plasticity, organic matter content, etc. Therefore, soils may not generally be free flowing materials that are easily removed or moved by conventional pneumatic transport. In some instances, special care may have to be taken in designing the vacuum transport system in order to avoid the persistent problem of cohesive materials clogging within the vacuum excavation system, such as that disclosed in U.S. Pat. No. 5,487,229.
In the literature for the design of industrial vacuum systems, conveying velocities and average soil densities for various materials are published and well known. For example, the average soil density for dry clay may be about 60 pounds per cubic foot and the average soil density for dry, packed sand and gravel may be as high as 120 pounds per cubic foot, and the recommended conveying velocities may range from 3,500 to 5,800 feet per minute for these types of materials. As a reference, 300 cubic feet per minute (cfm) of soil traveling through a 3-inch diameter hose translates to an air velocity of 6,100 feet per minute. In practice, however, if the soil is wet, higher conveying velocities ranging from 9,000 to 11,000 feet per minute may be needed.
There is a need, therefore, to provide a simpler and improved construction for an air powered vacuum apparatus in an air vacuum excavation system which uses an air nozzle to loosen the dirt or spoil and an air compressor for supplying air to the air nozzle and to the air powered vacuum.
There is also a need to provide an improved air powered vacuum apparatus in an air vacuum excavation system which is safe, efficient and easily operated.
There is still a further need to provide an air powered vacuum apparatus in an air powered excavation system that can pneumatically excavate and then transport any type of material, e.g. dirt, soil, sand, gravel, etc. regardless of its characteristics.